Most motorcycles in use today use a swingarm to locate the rear wheel relative to the motorcycle frame. The forward end of the swingarm pivots around a bolt running crosswise through the motorcycle frame or through brackets attached to the motorcycle frame to allow the rear wheel to move when it encounters a bump. The weight of the vehicle is supported by either one or two shock absorbers, which include a spring (mechanical or gas) and a means of damping the movement.
At one time, most motorcycle designs used two shock absorbers, with one shock absorber located on each side of the rear wheel and extending upward from the swingarm to the rearward part of the frame. In more recent years, a large number of designs using only one shock absorber have provided much better suspension performance. In such designs, the shock absorber is located forward of the wheel and extends from the area of the swingarm upward to an area under the forward portion of the seat. In many cases, the performance advantages of the single shock absorber designs are achieved by use of mechanical links at the top, the bottom, or both, which transmit the forces between the shock absorber and the frame and/or between the shock absorber and the swingarm. In these designs, either the upper end of the shock absorber and/or linkage and brackets uses space which could otherwise be used for an air filter box, a battery, or some other purpose.